There's 2 good players for mac, VLC & MPlayer. I'd recommend getting MPlayer also. http://mplayerosx.sourceforge.net/ or http://www.mplayerhq.hu/design7/dload.html

To change default, select the file, go to file menu, select Get Information. Then change the open with to VLC & click the Change All option. See sample here http://www.gnutellaforums.com/attach...6&d=1159739560